This invention relates to a static induction type thyristor and also to a process of producing the same.
In thyristors having the conventional PNPN four layer structure only one base region forming the control electrode has been disposed therein and is impossible to increase in impurity concentration resulting in an increase in base lateral resistance because the principal current flows through that base region. Further as the base region is coextensive with a cross section of a path for the principal current, it has increased distributed capacity. Accordingly the resulting RC time constant has been increased and the operating frequencies have been limited to the highest value on the order of 10 kilohertzs at most.
More specifically, upon transferring conventional thyristors from their blocking state to their conducting state (which is called hereinafter a "turn-on"), the spread of the semiconductor region in its ON state can not be rapidly controlled and therefore a corresponding turn-on time can not be short. This is because the base region has a large RC time constant. Also upon transferring such thyristors from their conducting to their blocking state (which is called hereinafter a "turn-off"), a long time is required until a very large number of majority and minority carriers having been injected into the junction in the ON state are moved through their diffusion to be absorbed by the particular electrode resulting in the extinction thereof. In addition, a turning-off voltage applied to the base region through a mating base electrode has been only effective for bringing that semiconductor region located adjacent to the base electrode into its OFF state without affecting any remote region spaced away from the base electrode. This is because the base region has a high lateral resistance. This has resulted in an increase in turn-off time. Sometimes turn-off has been impossible. Therefore direct currents have been scarcely possible to be interrupted. Even if possible, low capacity thyristors have been only enabled to interrupt low direct currents. In other words, conventional thyristors have been disadvantageous in very many respects such that the operation can not be performed at ultrahigh speeds with high electric powers, the high speed operation is performed with a low efficiency, direct currents are scarcely possible to be interrupted and so on.